JP3978507B2 - Bump inspection method and apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method and apparatus for inspecting bumps (projections) formed on the surface of a workpiece.
[0002]
[Prior art]
In mounting a semiconductor chip, bumps are used instead of wire bonding for the purpose of improving mounting density and connecting multiple pins. In the case of bump connection, the mounting time can be shortened compared to the lead wire connection, the mounting area can be reduced compared to the lead wire connection, and the signal arrival time can be shortened compared to the lead wire connection. This is because it has advantages.
By the way, in mounting using this bump, a large number of bumps are bonded together at corresponding locations on a mounting substrate such as a lead frame, so that the surface shape, formation position, width, and height of the bump are required to be appropriate. The This is even more so in today's highly integrated and miniaturized semiconductor integrated circuits.
Therefore, various bump inspection systems or bump inspection apparatuses for inspecting bumps of semiconductor substrates such as semiconductor wafers and semiconductor chips have been proposed today.
[0003]
[Problems to be solved by the invention]
However, types of bumps formed on the semiconductor substrate include ball bumps, straight bumps, and the like, and there has not been a bump inspection method and apparatus that can detect the height and shape of these types of bumps quickly and accurately.
[0004]
The present invention has been made in view of such problems, and an object of the present invention is to provide a bump inspection method and apparatus that can detect the height and shape of a bump quickly and accurately.
[0005]
[Means for Solving the Problems]
The bump inspection method according to claim 1, when inspecting the bump formed on the surface of the workpiece, the bump position on the design of the surface of the workpiece is irradiated with light from the normal direction of the surface of the workpiece, The actual bump position is detected from the light information obtained through the mask for the specular reflection component or the irregular reflection component of the reflected light, and the slit light is irradiated from the oblique direction to the actual bump position on the surface of the workpiece, and from the reflected light. The bump height or shape is detected from the obtained optical information.
In this case, the “mask” is preferably positioned at or near the focal plane position of the observation optical system for observing the reflected light. Further, for example, to obtain the optical information of the specular reflection component is observed vicinity of the optical axis of the optical system is transparent portion, the peripheral portion thereof are used mask is shielding portion, whereas, the optical information of the turbulent reflection component In order to obtain the above, a mask having a light shielding portion in the vicinity of the optical axis of the observation optical system and a light transmitting portion in the peripheral portion thereof is used. Furthermore, in order to detect bump height or shape by irradiation of slit light, for example, a well-known light cutting method is used. In this case, a single piece of slit light may be applied to each bump, but two or more pieces of slit light parallel to each other may be applied. Furthermore, all the bumps may be irradiated with slit light at once.
The “design bump position” refers to a bump position determined in the design when the bump is formed on the workpiece.
Moreover, it is preferable to use a digital mirror device or a transparent liquid crystal for forming the irradiation pattern for detecting the bump position or detecting the bump height or shape.
[0006]
According to such a bump inspection method, the actual bump position is detected from the regular reflection component or the irregular reflection component of the light reflected on the surface of the workpiece, and slit light is irradiated based on the bump position. Therefore, the bump height or shape can be accurately detected. Further, when the deviation between the actual bump position and the designed bump position is not within the allowable range, it is possible to determine that the bump is defective. On the other hand, if the deviation between the actual bump position and the design bump position is within the allowable range, or the deviation between the actual bump position and the design bump position is not within the allowable range, bump formation When necessary for process analysis, bump height and shape can be detected at the actual bump position.
[0007]
The bump inspection method according to claim 2, wherein, in the bump inspection method according to claim 1, when the bump is a bump having a spherical upper portion, the beam size of light irradiated from the normal direction is set to be larger than the size of the bump. The actual bump position is detected from light information that is made smaller and is a regular reflection component. The “spherical bumps on the upper part” are not particularly limited, but refer to ball bumps, mushroom bumps, and the like.
[0008]
According to this bump inspection method, when the surface of the workpiece is irradiated with light from the normal direction, when the upper part is a spherical bump, the specular reflection component of the reflected light is reflected at the top of the bump. Therefore, the actual bump position can be accurately detected mainly by obtaining optical information of the specular reflection component.
If the upper part is a spherical bump and the light beam size is larger than the bump size, not only the specular reflection component light information from the top of the bump but also the specular reflection component optical information from the workpiece surface. Thus, the image processing becomes complicated.
[0009]
The bump inspection method according to claim 3, wherein in the bump inspection method according to claim 1, when the bump is a straight bump, the beam size of light irradiated from the normal direction is made larger than the size of the straight bump. An actual bump position is detected from optical information which is a diffuse reflection component. “Straight bump” refers to a bump having a flat surface, such as a gold bump, but having a rougher surface than the workpiece surface. In this case, the “light beam dimension” is preferably determined in consideration of an allowable range of bump position deviation. For example, when the allowable range of the bump position deviation is exceeded, it is possible to easily determine whether the bump is defective or not by setting the beam size so that a regular reflection component from the top of the bump cannot be detected.
[0010]
According to this bump inspection method, when light is irradiated on the surface of the workpiece from the normal direction, in the case of a straight bump, the irregular reflection component of the reflected light is reflected on the upper surface of the bump. In addition, the actual bump position can be accurately detected by obtaining the light information of the irregular reflection component. Incidentally, the light reflected by the surface of the workpiece becomes a regular reflection component when the workpiece is a semiconductor wafer.
[0011]
The bump inspection apparatus according to claim 4, wherein the bump inspection apparatus inspects the bump formed on the surface of the work, and irradiates light on the design bump position on the surface of the work from the normal direction of the surface of the work. Then, the actual bump position is detected from the light information obtained through the mask for the regular reflection component or the irregular reflection component of the reflected light, and the actual bump position on the surface of the workpiece is irradiated with slit light from an oblique direction, A bump height or shape is detected from light information obtained from reflected light. In this case, although a single piece of slit light may be applied to each bump, a configuration in which two or more pieces of slit light parallel to each other may be applied. Furthermore, all the bumps (or all the bumps except those with defective bumps) may be irradiated with slit light at a time.
[0012]
According to such a bump inspection apparatus, the actual bump position is detected from the regular reflection component or the irregular reflection component of the light reflected on the surface of the workpiece, and the slit light is irradiated based on the bump position. Therefore, the bump height or shape can be accurately detected.
[0013]
A bump inspection apparatus according to a fifth aspect is the bump inspection apparatus according to the fourth aspect, wherein the irradiation pattern is formed by a spatial light modulator. Here, as the “spatial light modulator”, for example, a digital mirror device or a transparent liquid crystal can be considered.
[0014]
By using this spatial light modulator, the irradiation pattern can be easily changed.
[0015]
A bump inspection apparatus according to a sixth aspect is the bump inspection apparatus according to the fifth aspect, wherein the optical system for irradiating the slit light constitutes a Shine proof optical system.
[0016]
By using a shine-proof optical system as the optical system, it becomes possible to focus on the entire surface of the workpiece, and the bump height and shape can be detected more accurately.
[0017]
In addition, when irradiating slit light in the bump inspection method or apparatus, it is also possible to selectively irradiate wide or narrow slit light from an oblique direction on the surface of the workpiece. In this case, it is preferable that the width of the wide slit light is set to be larger than the width or diameter of the bump, and the width of the narrow slit light is set to be smaller than the width or diameter of the bump. Furthermore, in the case of narrow slit light, it is preferable to apply a plurality of parallel slit lights to the same bump. In this way, since a plurality of locations on the same bump can be inspected simultaneously, the inspection time can be shortened and the accuracy can be improved.
[0018]
In such a configuration, the surface of the workpiece is irradiated with wide or narrow slit light according to the type of bump. In this case, when a wide slit light is applied, a shadow of the bump is formed. By measuring the length of the shadow and the like, the bump height can be measured. The wide slit light is not particularly limited, but is particularly effective when inspecting ball bumps.
On the other hand, when narrow slit light is applied to the bump array portion, the bright portion corresponding to the upper surface of the bump and the bright portion corresponding to the base surface are misaligned. This misalignment amount reflects the bump height. The narrow slit light is not particularly limited, but is particularly effective when inspecting a straight bump.
[0019]
Moreover, in the said bump inspection method or apparatus, it is preferable to irradiate the slit light extended along the bump arrangement direction of a workpiece | work. By doing so, it is possible to inspect a plurality of arranged bumps simultaneously.
[0020]
Furthermore, in the bump inspection method or apparatus, it is preferable that the observation optical system for observing the reflected light of the slit light includes a line sensor as a light receiving unit. In this case, the extending direction of the line sensor is a direction orthogonal to the extending direction of the slit light, and it is preferable to inspect the bump by moving the line sensor in the extending direction of the slit light. According to this bump inspection apparatus, since light is received by the line sensor (one-dimensional sensor), inspection can be performed more quickly than in the case of using a two-dimensional sensor.
[0021]
DETAILED DESCRIPTION OF THE INVENTION
1. Configuration of Bump Measuring Device As shown in FIGS. 1 to 3, a bump measuring device according to the present invention includes a DMD (digital mirror device) 100 that can hold an arbitrary projection pattern, and a DMD illumination optical system 200 that illuminates the DMD 100. And a bump position measuring optical system 300 for measuring the bump position on the test surface 500 and a bump height measuring optical system 400 for measuring the bump height. In this case, the DMD 100 and the DMD illumination optical system 200 can be used both as a bump position detecting device for obtaining the bump position and a device for obtaining the bump height. In this case, for example, when the bump position is obtained by changing the angle of the entire DMD 100 and when the bump height is obtained, the bump position measuring optical system 300 and the bump height optical system 400 are What is necessary is just to set it as the structure which can be switched.
[0022]
2. Configuration of DMD 100 In the DMD 100 shown in FIGS. 1 to 3, each pixel arranged two-dimensionally is composed of a minute mirror, and the tilt of the minute mirror can be controlled by an electrostatic field effect by a memory element for each pixel. This is a reflective display element that creates an on / off state by changing the reflection angle of light from a mirror, and can hold an arbitrary projection pattern.
[0023]
3. Configuration of DMD Illumination Optical System 200 The DMD illumination optical system 200 shown in FIG. 1 includes a lamp 201, a reflecting mirror 202, a condenser lens 203, an integrator rod 204, and a condenser lens 205.
As the lamp 201, a halogen lamp, a metal halide lamp, a xenon lamp, or the like is used. An elliptical reflecting mirror is used as the reflecting mirror 202, and a lamp 201 is provided at one focal point of the elliptical reflecting mirror. Light from the lamp 201 is reflected by the reflecting mirror 202 to become parallel light. The condenser lens 203 collects the light from the reflecting mirror 202 and guides it to the integrator rod 204. The integrator rod 204 averages the luminous flux. The condenser lens 205 converts the light from the integrator rod 204 into parallel light. The DMD 100 is illuminated by this parallel light.
[0024]
4). Configuration of Bump Position Measuring Optical System 300 A bump position measuring optical system 300 shown in FIG. 4 includes a projection lens 301, an imaging lens 302, an objective lens 303, a half mirror 304, an imaging lens 305, a total reflection mirror 306, a connection lens. An image lens 307, a mask 308, an imaging lens 309, and a CCD 310 are provided.
The projection lens 301 projects the DMD 100 with the light as parallel light, and the imaging lens 302 is for imaging the light from the projection lens 301. The objective lens 303 converts the light from the imaging lens 302 into parallel light and irradiates the test surface 500, and forms an image of the light reflected by the test surface 500. The half mirror 304 is the objective lens 303. The light from diverges from the irradiation light. Further, the imaging lens 305 receives light from the half mirror 304, and the total reflection mirror 306 deflects the direction of light from the imaging lens 305. The imaging lens 307 is for imaging the light from the total reflection mirror 306, and the mask 308 is for blocking a part of the light from the imaging lens 307, and the focal point of the imaging lens 307. It is provided at the position (aperture surface). Further, the imaging lens 309 is for converting the light from the mask 308 into parallel light, and the CCD 310 receives the light from the imaging lens 309 and converts it into an electrical signal. The CCD 310 is preferably configured as a two-dimensional sensor.
[0025]
5). As the constituent mask 308 of the mask 308, as shown in FIG. 4, a ball bump mask 308a and a straight bump mask 308b are used. The ball bump mask 308a has a light transmitting part at the center and a light shielding part at the periphery, and blocks irregular reflection components on the test surface 500. On the other hand, the straight bump mask 308b has a light shielding portion at the center and a light transmitting portion at the periphery, and blocks the specular reflection component on the test surface 500. In this case, two types of masks, a ball bump mask 308a and a straight bump mask 308b, may be prepared and switched as necessary. However, by changing the mask pattern with a transparent liquid crystal plate, A bump mask 308a and a straight bump mask 308b may be configured.
Note that the mushroom bump mask may have the same configuration as the ball bump mask.
[0026]
6 Bump Position Measurement Principle (1) In Case of Ball Bump As shown in FIG. 5 (a), the ball bump 600 has a spherical shape at the top, so that the test surface 500 of a workpiece (for example, a semiconductor wafer) When light is applied from the normal direction, the light hitting the top part is specularly reflected, and the light hitting other places is irregularly reflected. Therefore, by observing only the specular reflection component of the light irradiated to the ball bump 600 and reflected there, the top position of the ball bump 600 and the bump position can be detected. In this case, it is preferable to apply a light beam (spot light) smaller than the size (diameter or dimension) of the ball bump 600 to the ball bump 600. This is because the surface of the test surface 500 on which the ball bump 600 is formed is a flat surface and is relatively smooth, so that the light hitting the flat surface is prevented from being simultaneously detected as a regular reflection component.
The same applies to mushroom bumps.
[0027]
(2) In the case of a straight bump As shown in FIG. 5 (b), the upper surface of the straight bump 700 is almost flat but the upper surface is rough (the roughness is high), so that the light hitting the upper surface is diffusely reflected. Ingredients. On the other hand, since the reflected light from the surface of the test surface 500 becomes a regular reflection component, the bump position can be detected by detecting the boundary. In this case, it is preferable to apply a light beam (area light) larger than the size (dimension) of the straight bump 700 to the straight bump 700.
[0028]
7). Configuration of Bump Height Measuring Optical System 400 A bump height measuring optical system 400 shown in FIG. 3 includes a projection lens 401, an objective lens 402, an imaging lens 403, and a CCD 404.
The projection lens 401 irradiates the test surface 500 with the light from the DMD 100 as parallel light. The DMD 100, the projection lens 401, and the test surface 500 constitute a Scheimpflug optical system. The reason why the Scheimpflug optical system is used is to adjust the optical path length from each part of the DMD 100 to the corresponding position of the test surface 500. The objective lens 402 forms an image of light from the test surface 500, and the imaging lens 403 receives the light from the objective lens 402. The CCD 404 receives light from the imaging lens 403 and converts it into an electrical signal. In this case, the CCD 404 is preferably configured as a line sensor. A stop 405 is provided at the stop position between the objective lens 402 and the imaging lens 403, and these constitute a double-sided telecentric optical system. In this telecentric optical system, the aperture angle is narrowed, thereby increasing the depth of focus.
[0029]
8). Example of Bump Height Measurement Principle Based on bump position data obtained by the bump position measuring optical system 300, the arrangement pitch of bumps formed on the test surface 500 is obtained by image processing by a computer.
[0030]
Next, it is selected whether to use a wide slit light or a narrow slit light according to the type of bump. Specifically, when the bump type is a ball bump or mushroom bump, a wide slit light is selected. In other cases, that is, when the bump type is a straight bump, a narrow slit light is selected. Since the bump arrangement pitch has already been obtained, the scanning speed of the one-dimensional sensor (line sensor: constituted by the CCD 404) is calculated by the computer from the arrangement pitch.
[0031]
In this case, when a wide slit light is selected, a wide slit light about twice the diameter of the bump is controlled with the incident angle θ (for example, 45 °) as shown in FIG. The surface 500 is irradiated, and the optical image of the test surface 500 is captured with the reflection angle θ (for example, 45 °) by the bump height measurement optical system 400. At this time, the one-dimensional sensor is moved in the extending direction of the slit light.
[0032]
The situation at this time is shown in FIGS. However, FIGS. 6 and 7 show straight bumps as an example for convenience of explanation. At this time, the shadow of the bump 600 is formed by the light hitting the bump 600. The height of the bump is obtained from the length of the shadow by a computer. In the case where the bump is the ball bump 700, the shadow of the bump 700 is formed by the light hitting the bump 700, while the vertex of the bump 700 becomes a bright spot, so the computer calculates from the shadow length and the position of the bright spot. Can be used to determine the height of the bump.
[0033]
7A shows a cross-sectional view of the bump taken along the line AA in FIG. 7B. The peak portion indicates the bump, and the valley portion indicates the base surface of the test surface 500. FIG.
[0034]
On the other hand, when narrow slit light is selected, light having a width of about one quarter of the diameter of the bump 600 is controlled with the incident angle θ (for example, 45 °) as shown in FIG. The test surface 500 is irradiated, and the optical image of the test surface 500 is captured with a reflection angle θ (for example, 45 °) by the bump height measurement optical system 400. At this time, the one-dimensional sensor 32 is moved in the extending direction of the slit light.
[0035]
The situation at this time is shown in FIGS. However, FIG. 8 and FIG. 9 show the straight bump 600 as an example for convenience of explanation. At this time, as shown in FIG. 8 and FIG. 9B, the position of the slit light in the optical image (bright part) is shifted between the part that hits the bump 600 and the part that hits the surface (base) of the test surface 500. This positional deviation amount reflects the bump height. Therefore, the bump height can be obtained by measuring the positional deviation amount of the optical image.
[0036]
9A shows a cross-sectional view of the bump taken along the line AA in FIG. 9B, and the valley portion shows the surface of the test surface 500. FIG.
[0037]
9. Example of Bump Inspection Process (1) In Case of Ball Bump First, design bump position data is read into a computer (S1). Based on the bump position data, spot light is irradiated to the bump position in the design of the surface 500 to be inspected (S2). In this case, the spot light irradiation pattern is formed by controlling the mirror of the DMD 100 by a computer processing device. Then, the actual bump position is obtained by the processing device of the computer from the light information of the specular reflection component of the reflected light from the test surface 500. Next, a deviation amount between the designed bump position and the actual bump position is calculated by a computer processing device to determine whether the bump is good or bad. When a defective bump is found, the entire workpiece may be regarded as defective, and detection of the bump height may be stopped for the workpiece, but the height of only good bumps may be measured. In this case, slit light is applied to the good bumps on the test surface 500 based on the bump position data of the good bumps. In this case, the spot light irradiation pattern is formed by controlling the mirror of the DMD 100 by a computer processing device. Then, the bump height is calculated by the processing device of the computer from the optical information that is the reflected light from the test surface 500.
On the other hand, when the bump height of the defective bump is also detected, slit light is irradiated to the defective bump on the test surface 500 based on the actual bump position data of the defective bump. In this case, the spot light irradiation pattern is formed by controlling the mirror of the DMD 100 by a computer processing device. Then, the bump height is calculated by the processing device of the computer from the optical information that is the reflected light from the test surface 500.
Note that the bump inspection is performed in the same manner when the mushroom bump is used instead of the ball bump.
[0038]
(2) In the case of a straight bump In the case of a straight bump, the bump inspection is performed in substantially the same process except that the area light is irradiated instead of the spot light.
[0039]
9. Configuration of an Example of Bump Inspection System FIG. 10 shows a bump inspection system in which the bump measuring device is incorporated.
This bump inspection system includes a bump position measuring device 800 and a bump height measuring device 900. In this bump inspection system, the DMD 100 of the bump position measuring device 800 and the bump height measuring optical system 900 is controlled by the host computer 1000 via the DMD controllers 2100 and 2200. The CCDs 310 and 404 are connected to the image processing unit 1300 via the CCD controllers 1100 and 1200, and the image processing unit 1300 is connected to the host computer 1000. In the figure, reference numeral 1400 denotes an XYθ stage, which is connected to the host computer 1000 via an XYθ stage controller 1500. Reference numeral 1600 denotes an XZ stage, which is connected to the host computer 1000 via the XZ stage controller 1700. Reference numeral 1800 is a monitor, and reference numeral 1900 is a CRT.
[0040]
As mentioned above, although embodiment of this invention was described, it cannot be overemphasized that a various deformation | transformation is possible for this invention in the range which is not limited to this embodiment and does not change the summary.
[0041]
【The invention's effect】
Explaining the effect of the representative one of the present invention, since the bump position is obtained and then the bump height is obtained, the bump height can be accurately detected.
[Brief description of the drawings]
FIG. 1 is a configuration diagram of an optical system for DMD illumination according to an embodiment.
FIG. 2 is a configuration diagram of an optical system for bump position measurement according to the embodiment.
FIG. 3 is a configuration diagram of an optical system for bump height measurement according to the embodiment.
FIG. 4 is a configuration diagram of a mask according to the embodiment.
FIG. 5 is a diagram showing a bump position measurement principle according to the embodiment.
FIG. 6 is a diagram illustrating an operation when a wide slit light is applied.
FIG. 7 is a diagram for explaining how a bump shadow appears when a wide slit light is applied.
FIG. 8 is a diagram showing an operation when narrow slit light is applied.
FIG. 9 is a diagram for explaining an optical image when narrow slit light is applied.
FIG. 10 is a configuration diagram of a bump inspection system.
100 DMD
200 DMD illumination optical system 300 Bump position measurement optical system 400 Bump height measurement optical system 500 Test surface 600 Ball bump 700 Straight bump

Claims (6)

  In inspecting the bump formed on the surface of the workpiece, the design bump on the surface of the workpiece is irradiated with light from the normal direction of the surface of the workpiece, and the regular reflection component or irregular reflection of the reflected light is irradiated. The actual bump position is detected from the light information obtained through the mask of the component, the slit light is irradiated from the oblique direction to the actual bump position on the surface of the workpiece, and the bump height or shape is obtained from the light information obtained from the reflected light. Detecting a bump.   When the bump is a bump having a spherical upper part, the beam size of light irradiated from the normal direction is made smaller than the size of the bump, and the actual bump position is detected from the optical information which is a specular reflection component. The bump inspection method according to claim 1, wherein:   When the bump is a straight bump, the beam size of light irradiated from the normal direction is made larger than the dimension of the straight bump, and an actual bump position is detected from optical information that is a diffuse reflection component. Item 1. A bump inspection method according to Item 1.   In the bump inspection apparatus for inspecting the bump formed on the surface of the work, the bump position on the design of the work surface is irradiated with light from the normal direction of the surface of the work, and regular reflection of the reflected light The actual bump position is detected from the light information obtained through the mask for the component or the diffuse reflection component, the actual bump position on the surface of the workpiece is irradiated with slit light from an oblique direction, and the bump height is determined from the light information obtained from the reflected light. A bump inspection apparatus for detecting a thickness or a shape.   The bump inspection apparatus according to claim 4, wherein the irradiation pattern is formed by a spatial light modulator.   6. The bump inspection apparatus according to claim 5, wherein the optical system for irradiating the slit light constitutes a Scheimpflug optical system.

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